737 Flight Crew Operations Manual
Warning Systems -
System Description
Boeing Proprietary. Copyright © Boeing. May be subject to export restrictions under EAR. See title page for details.
15.20.8 D6-27370-866-EGP
Stall Warning System
Natural stall warning (buffet) usually occurs at a speed prior to stall. In some
configurations the margin between stall and natural stall warning is less than
desired. Therefore, an artificial stall warning device, a stick shaker, is used to
provide the required warning.
The stall warning “stick shaker” consists of two eccentric weight motors, one on
each control column. They are designed to alert the pilots before a stall develops.
The warning is given by vibrating both control columns. The system is armed in
flight at all times. The system is deactivated on the ground.
Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.
Altitude Alerting System
Altitude alerting occurs when approaching or departing the MCP–selected
altitude. Altitude alerting is inhibited when trailing edge flaps are extended to 25
or greater, or while G/S is captured.
PFD/ND
Acquisition Alerting
900 feet before reaching the selected altitude, a white box shows around the
selected altitude display and the box around the current altitude becomes bold. A
momentary tone sounds. At 300 feet from selected altitude, the selected altitude
box no longer shows.
September 26, 2013
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